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Re: Access to single object from multiple other objects

by tobyink (Abbot)
on Oct 31, 2013 at 08:56 UTC ( #1060542=note: print w/replies, xml ) Need Help??


in reply to Access to single object from multiple other objects

Singletons and global variables are both manifestations of "global state". Generally speaking, global state is the enemy. (And I don't mean that as an anti-UN conspiracy theorist!)

If the global state is mutable (i.e. different parts of the code can alter it), then it can result in spooky action at a distance. Even if it's immutable, it can result in too tight coupling between different bits of code.

It's certainly best to pass into functions all the data they need to do their job, and pass to object constructors all the data the object needs.

It can be cumbersome to pass around database handles from object to object, but there are patterns that can be followed to help eliminate some of these difficulties. For example, say you have a Document object that creates several Section objects, and needs to pass its database handle on to its sections. You might have something like this...

sub get_header { my $self = shift; Section->new(dbh => $self->dbh, title => "Header"); } sub get_toc { my $self = shift; Section->new(dbh => $self->dbh, title => "Contents"); } sub get_footer { my $self = shift; Section->new(dbh => $self->dbh, title => "Footer"); }

This can be transformed into:

sub make_section { my $self = shift; Section->new(dbh => $self->dbh, @_); } sub get_header { my $self = shift; $self->make_section(title => "Header"); } sub get_toc { my $self = shift; $self->make_section(title => "Contents"); } sub get_footer { my $self = shift; $self->make_section(title => "Footer"); }

This means that the dbh pass-the-parcel happens in just one place instead of many. It also makes it easier for subclasses of Document to override the construction of Section objects.

(My module MooseX::ConstructInstance can help with implementing this pattern.)

use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name

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[Discipulus]: marioroy did you know zentara is back to themonastery? he was used to be one of the best parallel programming monks
[makita]: sign_types parameter in XML::Compile::WSS ::Signature Does have anybody experience how to use it?
[makita]: Need to sign more elements but all types I put in array are ignored. And is always signed only the body
[Discipulus]: no makita sorry. i see in the synopsis of the module: "WARNING: Only limited real-life experience" might be better compose a SOPW with some code example and data
[Discipulus]: ..or inspect the source code of the module
[makita]: I am doing this:
[makita]: my $sig = $wss->signature( schema => $wsdl, token => $token, sign_types=>'wsa: Action','wsa:To', 'wsu:Timestamp', 'wsa:MessageID',' SOAP-ENV:Body', signer=>DSIG_RSA_S HA1, public_key => $cert,
[Corion]: Oof, I haven't done much with signing SOAP requests. markov is usually somebody good to ask via mail ;)
[makita]: I need to create a SOAP call where are signed more types not only the body

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